Multilayer non-woven fabric and use thereof

ABSTRACT

A multilayer non woven fabric having a polypropylene spun bonded non woven fabric and a polypropylene melt blown non woven fabric, characterized in that it has a bending resistance, the sum of the values for longitudinal and transverse directions as measured according to JIS L 1096 6. 19.1 A method (45 degree cantilever method) of 70 to 120 mm, the surface of the spun bonded non woven fabric has a static friction coefficient of 0.1 to 0.4. The multilayer non woven fabric preferably has a polypropylene melt brown non woven fabric layer between polypropylene spun bonded non woven fabric layers.

TECHNICAL FIELD

[0001] The present invention relates to a multi layer non woven fabric,and relates to a multi layer non woven fabric made of a polypropylenebased resin which has a liquid barrier property, fine powder barrierproperty and gas permeability, particularly is excellent in feeling andskin touch feeling and in strength and secondary processability, and canbe suitably used for various applications, particularly, back sheetmaterials and side gather materials for absorptive articles such asdispensable diapers and the like and medical and powder wrappingmaterials and the like, and to a use thereof.

BACKGROUND ART

[0002] Spun bonded non woven fabrics are used in a lot of fields becauseof excellent continuous spinning and productivity together withproperties such as excellent strength, suitable bending resistance, gaspermeability and the like. As the thermoplastic resin used in this spunbonded non woven fabric, long fiber non woven fabric, polyamide basedresins and polyester based resins have been used due to a melt spinningproperty, fiber property and the like, however, polypropylene basedresins, common resins, are being used frequently in absorptive articlessuch as disposable diapers and the like.

[0003] These polypropylene based resin non woven fabrics include a lotof resins different in crystallinity even in the case of homopolymers ofpropylene, and there are known non woven fabrics made of resins havingvarious properties such as melting point, strength, elastic modulus andthe like by a copolymer of propylene with ethylene, butene-1 and thelike. Such a non woven fabric using a polypropylene based resin has, inthe case of a resin having high crystallinity, an excellent spinningproperty, however, is inferior in flexibility and has a problem infeeling. In the case of a propylene based resin having low crystallinityor melting point, flexibility is obtained, however, there are problemsthat a slimy feeing occurs, friction resistance between fibers, betweenfiber and other metals and the like in spinning increases, leading to anextremely poor spinning property.

[0004] At present, as the polypropylene based resin non woven fabricused in absorptive articles such as disposable diapers and the like,there are frequently used those produced by using a resin having anisotactic pentad fraction of about 90 mol %, index of crystallinity, dueto strength, spinning property, rigidity and the like thereof.

[0005] However, there is a problem that the use feelings such asflexibility, feeling, skin tough and the like of the resulted non wovenfabric are not necessarily sufficient when used in absorptive articlessuch as disposable diapers, sanitary napkins, incontinence pads and thelike

[0006] Though a spun bonded non woven fabric made of this polypropylenebased resin long fiber is a material excellent in gas permeability, aliquid barrier property, in use as the absorptive article, is anessential required property particularly in a back sheet for absorptivearticles, depending on use places. Therefore, for satisfying the liquidbarrier property and property of a polypropylene based resin non wovenfabric simultaneously, generally used are non woven fabric complexmaterials obtained by complexing with other moisture permeable waterpreventing materials. Likewise, a side gather is also used in complexwith materials having excellent water pressure resistance.

[0007] However, an absorptive article using this non woven fabriccomplex material comes in direct contact with skin, and with clothes inuse, or comes in contact with hands of workers in detaching. Therefore,it is suggested that use feelings such as flexibility, feeling, skintouch and the like and a working feeling are not satisfactory, and itstouch feeling is as of a plastic film, and not suitable also for skin.Accordingly, non woven fabric laminates having improved these propertiesare desired.

[0008] For this, there are suggested various improvements in thefeeling, skin tough feeling and the like as the surface material ofthese absorptive articles. For example, (1) Japanese Patent ApplicationLaid Open (JP-A) No. 2-88056 suggests that a polyolefin based melt blownnon woven fabric having a fineness of less than 1 denier and having amass per unit area (Metsuke) of 0.2 go 10 g/m² is contacted with andlaminated on a polyolefin based spun bonded non woven fabric having afineness of 1 to 4 denier and having a mass per unit area of 8 to 28g/m² when the non woven fabric shows stickiness. However, though aneffect is observed in the case if a spun bonded non woven fabric havinga narrow fiber diameter, when the fiber diameter decreases, the bendingresistance of a spun bonded non woven fabric lowers, and working is notstable in steps of running of a laminate, heat sealing, and the like,and high speed processing and automation may become difficult, insecondary processes.

[0009] (2) JP-A No. 9-143853 suggests a laminated non woven fabricobtained by fusing a complex spun bonded non woven fabric made of twokinds of resins having a melting point difference of 10° C. or more totwo kinds of melt blown non woven fabrics having a melting pointdifference of 10° C. or more, with a resin of low melting point and anon woven fabric. However, in this case, feeling is generated by themelt blown non woven fabric and is a property as the surface material ofthe melt blown non woven fabric, consequently, a problem of the meltblown non woven fabric cannot be solved, and in the production of thecomplex non woven fabric, an apparatus becomes complicated, and meltingpoint and flowability are different between the complex resins, leadingto difficulty in spinning, in some cases.

[0010] Further, (3) JP-A No. 10-16115 suggests a moisture permeable filmobtained by heat fusing a gas permeable film to a non woven fabric (spunbonded) containing a resin having melting point lower than or the sameas that of a resin in the above mentioned gas permeable film, at anemboss are ratio of 5 to 20% by emboss processing of an emboss patternhaving no angle. However, in this case, resins to be combined arelimited, and the spun bonded non woven fabric itself is not particularlyimproved, therefore, it is estimated that improvements in surfaceproperty and feeling are limited.

[0011] Furthermore, (4) JP-A No. 11-972 suggests a moisture permeablecomplex film obtained by laminating a polyolefin based non woven fabrichaving a mass per unit area of 5 to 20 g/m², an average fiber diameterof 0.2 to 2 denier and a bulk specific gravity of 0.05 or less on atleast one surface of a polyolefin based biaxially stretched moisturepermeable film. However, this complex film is composed mainly of amoisture permeable stretched film, the non woven fabric itself is aspecial material that is, the complex film is a special film which isnot a general laminate mainly composed of a spun bonded non wovenfabric.

[0012] Still further, (5) JP-A No. 11-290381 discloses a back sheet forabsorptive article in which a polypropylene based wet non woven fabriclayer constitutes one of surface layers of a laminate obtained byalternately laminating a layer made of a polypropylene based melt blownnon woven fabric and a layer made of a polypropylene based wet non wovenfabric. Namely, by adoption of a short fiber wet non woven fabric, asurface sliding property and a liquid barrier property are intended tobe secured. However, the fiber diameter of a wet non woven fabric isrelatively narrow, and a problem occurs that a production method becomescomplicated.

[0013] As described above, the moisture permeable water preventing nonwoven fabric complex material does not hold properties in performancesuch as strength, flexibility, bending resistance and the like andfeatures in production such as a spinning property and cheapness, ofconventional polypropylene based resin spun bonded non woven fabrics,and only provides fine fiber diameter, soft resin use, short fiber,complex spinning and the like.

[0014] Therefore, these improvement technologies have a maximum problemin that a secondary processability which is an important property in useof a spun bonded non woven fabric in large amount in disposable diapersand the like, namely, suitable bending resistance necessary for handinga non woven fabric stably in complexing processes such as transferringof a non woven fabric, heat adhesion and the like is not maintained.Therefore, it is difficult to speed up, automation and stable productionin production of an absorptive article.

[0015] Consequently, particularly due to secondary processabilities andproductivities such as a spinning property and the like, complexmaterials with a polypropylene spun bonded non woven fabric are stillused in spite of insufficient feeling, skin touch and the like, as thenon woven fabric complex material, in current conditions. Therefore,improvement of these problems of polypropylene spun bonded non wovenfabrics is strongly desired by users and producers of absorptivearticles such as disposable diapers and the like.

[0016] An object of the present invention is to provide a moisturepermeable water preventing multi layer non woven fabric substantiallyholding properties such as strength, secondary processabilities and thelike essentially revealed by polypropylene based resin spun bonded nonwoven fabrics, and additionally having excellent flexibility, feeling,skin touch feeling and the like, particularly, a multi layer non wovenfabric which can be suitably used for back sheets and side gathers ofabsorptive articles such as disposable diapers, sanitary napkins and thelike, and for medical and powder wrapping materials and the like, and ause thereof.

DISCLOSURE OF THE INVENTION

[0017] The present inventors have intensively studied use feelingsrequired for non woven fabric final articles, particularly, forabsorptive articles and the like, such as flexibility, feeling, skintouch feeling and the like, regarding non woven fabric materials endowedwith a water preventing property and a powder barrier property, whileutilizing functions such as gas permeability, flexibility, strength,heat resistance, secondary processability, automation fitness and thelike of polypropylene based resin spun bonded non woven fabrics. As aresult, the present inventors have found that even a spun bonded nonwoven fabric can remarkable improve use feelings such as flexibility,feeling, skin touch and the like as compared with conventional multilayer non woven fabrics even if resin used, fiber diameter and mass perunit area are equivalent, by controlling its friction property and bycomplex with a melt blown non woven fabric, leading to completion of theinvention based on this finding.

[0018] Namely, the present invention provides

[0019] (1) A multi layer non woven fabric having a polypropylene basedresin spun bonded non woven fabric and a polypropylene based resin meltblown non woven fabric, characterized in that it has a bendingresistance [the sum of the values for longitudinal and transversedirections as measured according to JIS L 1096 6. 19.1 A method (45°cantilever method)] of 70 to 120 mm, and the surface of the spun bondednon woven fabric has a static friction coefficient of 0.1 to 0.4;

[0020] (2) The multi layer non woven fabric according to (1) wherein themulti layer non woven fabric has a polypropylene based resin melt blownnon woven fabric between propylene based resin spun bonded non wovenfabrics;

[0021] (3) The multi layer non woven fabric according to (1) or (2)wherein the spun bonded non woven fabric has an average fiber diameterof 10 to 30 μm and the mass per unit area of the multi layer non wovenfabric is from 10 to 50 g/m²;

[0022] (4) The multi layer non woven fabric according to any of (1) to(3) wherein the spun bonded non woven fabric contains a lubricant in anamount of 0.05 to 1.0% by weight;

[0023] (5) The multi layer non woven fabric according to any of (1) to(4) wherein the lubricant is a fatty amide compound;

[0024] (6) An absorptive article obtained by using the multi layer nonwoven fabric according to any of (1) to (5);

[0025] (7) A medical sheet obtained by using the multi layer non wovenfabric according to any of (1) to (5); and

[0026] (8) A powder wrapping material obtained by using the multi layernon woven fabric according to any of claims (1) to (5).

BEST MODES FOR CARRYING OUT THE INVENTION

[0027] The present invention will be illustrated in detail below.

[0028] The multi layer non woven fabric is a multi layer non wovenfabric having a polypropylene based resin spun bonded non woven fabricand a polypropylene based resin melt blown non woven fabric,characterized in that it has a bending resistance [the sum of the valuesfor longitudinal and transverse directions as measured according to JISL 1096 6. 19.1 A method (45° cantilever method)] of 70 to 120 mm, andthe surface of the spun bonded non woven fabric has a static frictioncoefficient of 0.1 to 0.4.

[0029] Namely, it is a multi layer non woven fabric having apolypropylene based resin spun bonded non woven fabric constituting atleast one surface of the multi layer non woven fabric, and apolypropylene based resin melt blown non woven fabric, in which it has abending resistance [the sum of the values for longitudinal andtransverse directions as measured according to JIS L 1096 6. 19.1 Amethod (45° cantilever method)] of 70 to 120 mm, and the surface of thespun bonded non woven fabric has a static friction coefficient of 0.1 to0.4.

[0030] The multi layer non woven fabric of the present invention can beproduced by inline or secondary connection of a polypropylene basedresin spun bonded non woven fabric having a static friction coefficientof 0.1 to 0.4 and a polypropylene based resin melt blown non wovenfabric. Preferable is a multi layer non woven fabric of three layerstructure having a polypropylene based resin melt blown non woven fabricsandwiched by polypropylene based resin spun bonded non woven fabrics.

[0031] Materials constituting the multi layer non woven fabric of thepresent invention will be described below.

[0032] [Polypropylene Based Resin Spun Bonded Non Woven Fabric]

[0033] The polypropylene based resin spun bonded non woven fabric mayadvantageously be that having a static friction coefficient within arange from 0.1 to 0.4. Therefore, the means of controlling the staticfriction coefficient is optional, and adoption of various means isconsidered. However, the reason for a fact that the multi layer nonwoven fabric of the present invention has excellent flexibility, feelingand skin touch feeling is believed to an effect by improvement of asliding property of mutual long fibers in a spun bonded non wovenfabric, therefore, it is preferable that not only a fiber slidingproperty of the surface part of a non woven fabric but also a fibersliding property of the whole non woven fabric is improved andresultantly, the static friction coefficient as a surface property iswithin a specific range.

[0034] The fiber diameter of a polypropylene based resin spun bonded nonwoven fabric constituting the multi layer non woven fabric of thepresent invention is preferably from 10 to 30 μm, more preferably from15 to 25 μm. Here, when less than 10 μm, strength and bending resistancelower and secondary processabilities lower in come cases, and its usefield is restricted significantly. While when over 30 μm, flexibility,feeling and skin tough feeling lower, and the features of the presentinvention as a multi layer non woven fabric lose, and particularly,application to absorptive articles, medical materials, wrapping bodiesand the like is difficult in some cases.

[0035] The mass per unit area of the polypropylene based resin spunbonded non woven fabric in the multi layer non woven fabric ispreferably from 5 to 40 g/m², more preferably from 7 to 30 g/m². Here,when the mass per unit area is less than 5 g/m², strength is notsufficient, bending resistance is low, and secondary processabilitiesare inferior in some cases, while when over 40 g/m², flexibility, gaspermeability, skin touch feeling and the like decrease, the features ofthe present invention as a multi layer non woven fabric lose, anddepending on applications, use is difficult in some cases. This mass perunit area of the polypropylene based resin spun bonded non woven fabricis that when the spun bonded non woven fabric exists as a single layerin the multi layer non woven fabric, and in the case of two layers, theabove mentioned mass per unit area is the sum of the mass per unit areaof the two layers.

[0036] The second feature of the multi layer non woven fabric of thepresent invention is that the polypropylene based resin spun bonded nonwoven fabric has a static friction coefficient of 0.1 to 0.4, preferably0.12 to 0.35. Here, when the static friction coefficient is less than0.1, processabilities decrease due to excess sliding in secondaryprocessing, and because of decrease in the static friction coefficient,the use amount of additives or surface treatment agents generallyadopted is required to be large, deteriorating in economy, in somecases. Further, a connecting property by heat seal, additives and thelike in secondary processing tends to decrease undesirably, in somecases. When over 0.4, an effect of improving use feelings such asflexibility, feeling, skin touch feeling and the like is insufficient.Polypropylene based resin spun bonded non woven fabrics can beappropriately selected and combined based on applications in which amulti layer non woven fabric is used, necessary conditions, gaspermeability, water resistance (non water permeability) and the like.

[0037] The static friction coefficient of the surface of the multi layernon woven fabric of the present invention can be measured according toASIM-D1894. Specifically, based on the following measurement conditions:

[0038] Static friction coefficient measuring apparatus: AN typemanufactured by Toyo Seiki Seisakusho K.K.

[0039] Load plate: iron plate of 63.6 mm×102.2 mm×19.4 mm (height) andload: 8.87 N

[0040] Inclination speed: 2.7°/second,

[0041] measurement surfaces of non woven fabrics are mutually overlaid,sliding angle (θ) is measured, tan θ is measured, to give a staticfriction coefficient. When the numerical value is smaller, a slidingproperty is more excellent.

[0042] The polypropylene based resin used in the polypropylene basedresin spun bonded non woven fabric used in the multi layer non wovenfabric of the present invention is not particularly restricted, andlisted are homopolymers of propylene, and copolymers of propylene withat least one of α-olefins such as ethylene, butene-1,4-methyl-pentene-1,hexane-1, octane-1 and the like. As these polypropylene based resins,various resins different in crystallinity, molecular weight andmolecular weight distribution are appropriately selected based onconditions required for a non woven fabric, depending on selection,polymerization conditions and the like of a catalyst in polymerization.This selection is investigated from the standpoints of the strength,flexibility, application and the like of a non woven fabric, and asdescribed above, there are used homopolymers of propylene orpolypropylene copolymers having a copolymerization ratio of preferably 5wt % or less, more preferably 3 wt % or less, in view of a spinningproperty, flexibility, slimy feeling and the like.

[0043] Here, regarding crystallinity, when a non woven fabric is used asa material for absorptive article such as disposable diapers and thelike, the isotactic pentad fraction is preferably selected in the rangeof from 88 to 95 mol %, more preferably from 89 to 93 mol %. Here, theisotactic pentad fraction (IPF) is an isotactic pentad fraction inpentad unit in a polypropylene molecule chain measured using nuclearmagnetic resonance spectrum (¹³C-NMR) by isotope carbon described, forexample, in “Macromolecules”, vol. 28, no. 16, p. 5403 (1995).

[0044] The melt flow rate (MFR) [according to JIS K 7210, measurementtemperature: 230° C., measurement load: 21.18 N] of a polypropylenebased resin is in the range of from 5 to 200 g/10 minutes, preferablyfrom 10 to 100 g/10 minutes. Particularly, as the absorptive article,those having a melt flow rate in the range of from 30 to 80 g/10 minutesare suitable.

[0045] Next, the means for obtaining a polypropylene based resin spunbonded non woven fabric having a static friction coefficient of 0.1 to0.4, which is a feature of the present invention, is not particularlyrestricted, and various means are listed. Specifically, these areroughly classified into (1) methods of compounding a lubricant in apolypropylene based resin for spinning, conducting melt spinning, then,effecting aging, (2) methods of conducting surface treatment on fibersafter spinning, and the like, for example.

[0046] Here, the lubricant is not particularly restricted, and there arementioned fatty amide compounds, fatty acid compounds, paraffin andhydrocarbon resins, silicone based compounds, silicone based polymers,fluorine based compounds, fluorine based polymers such as copolymers oftetrafluoroethylene with propylene, copolymers of vinylidene fluoridewith hexafluoropropylene, and the like; or mixtures thereof. Of them,fatty amide compounds are preferably used.

[0047] As the fatty amide compound, listed are fatty monoamidecompounds, fatty diamide compounds, saturated fatty monoamide compounds,and unsaturated fatty diamide compounds. Specifically listed are lauricamide, myristic amide, palmitic amide, stearic amide, behenic amide,oleic amide, erucic amide, montanic amide, N,N′-methylene-bis-lauricamide, N,N′-methylene-bis-myristic amide, N,N′-methylene-bis-palmiticamide, N,N′-methylene-bis-behenic amide, N,N′-methylene-bis-oleic amide,N,N′-methylene-bis-erucic amide, N,N′-ethylene-bis-oleic amide,N,N′-ethylene-bis-erucic amide and the like, and it is also possible touse two or more of them in combination.

[0048] These fatty amide compounds, among them, erucic amide which is anunsaturated fatty monoamide compound is preferably used. The reason forthis is that because of decrease in a spinning property by unnecessaryprojection of a fatty amide onto the surface in melt spinning of a nonwoven fabric, and of aging of a non woven fabric containing a fattyamide compound described later, erucic amide is suitable for decrease inthe static friction coefficient of a non woven fabric. The content ofthis fatty amide compound is in the range of from 0.05 to 1 wt %,preferably from 0.1 to 0.7 wt % in a polypropylene based resin. Thiscontent is determined by totally judging the kind of a polypropylenebased resin, resin properties thereof such as crystallinity, MFR and thelike, the kind of a fatty amide compound, required conditions of theresulting non woven fabric, aging conditions and the like.

[0049] Therefore, for example, as a homopolymer of propylene, theisotactic pentad fraction is about 90 mol %, and when erucic amide isused, it is in the range of from 0.1 to 1.0 wt %, preferably from 0.2 to0.6 wt %. In this case, depending on aging treatment conditions, whenless than 0.1 wt %, it may be difficult to control the static frictioncoefficient of a non woven fabric in the range from 0.1 to 0.4, and whenover 1.0 wt %, the amount of erucic amide on the surface of a non wovenfabric increases, and deteriorations in appearance such as white powdergeneration and the like and decrease in a heat fusion property andsecondary processabilities are caused, in some cases.

[0050] In a polypropylene based resin, there can be added known additivecomponents generally used in non woven fabrics for applications of amulti layer non woven fabric, endowment of properties, and the like. Asthese known additive components, listed are neutralization agents suchas calcium stearate, hydrotalcite and the like, phenol based, phosphorusbased and sulfur based antioxidants and the like, heat stabilizers,nucleating agents, ultraviolet absorbers, light stabilizers, antistaticagents, flame retardants, pigments, dyes, or inorganic powders such assilica, talc, calcium carbonate, calcium oxide, magnesium oxide and thelike.

[0051] In one example of a method of producing a spun bonded non wovenfabric constituting the present invention, a polypropylene based resinis melt spun with a mixture obtained by dry blending a given amount oflubricant such as a fatty amide and the like with additive componentsadded if necessary.

[0052] The polypropylene based resin spun bonded non woven fabric use inthe multi layer non woven fabric of the present invention is notparticularly restricted, and can be produced by known various productionmethods. For example, a primary non woven fabric can be obtained by aknown production method in which a polypropylene based resin, rawmaterial for the above mentioned compounding, is melt extruded from anextrusion molding machine, spun through a spinning mouth ring, and thespun fiber is drawn by a gas flow traction apparatus such as an airsucker and the like, if necessary, fibers are opened and fiber arecollected by a web collecting apparatus together with gas flow, and ifnecessary, partially welded by heating means such as heated air, heatroll and the like, particularly by a heat roll, then, taken.

[0053] As the bonding mode, heat adhesion such as emboss, calender, hotair and the like, adhesion with adhesives, and mechanical entanglingsuch as needle punch, water punch and the like can be adopted. However,heat adhesion by embossing is preferable from the standpoint ofproductivity or the like.

[0054] This polypropylene based resin spun bonded non woven fabric isusually a non woven fabric made of a polypropylene based resin singlebody, and at least 50% or more of the outer surface of fibers may alsobe a complex fiber non woven fabric made of a polypropylene based resin.

[0055] These complex fiber non woven fabric can also be a complex fiberof core sheath structure composed of a polypropylene based resin as asheath component and a resin other than the polypropylene based resin,such as a polyamide based resin, polyester based resin and the like, ora complex fiber of side by side structure in which usually 50 wt % ormore of fibers are made of a polypropylene based resin and remainingparts are made of other resins. This core sheath structure complex fiberand side by side structure complex fiber may comprise a combination oftwo different polypropylene based resins among polypropylene basedresins, of course.

[0056] Thus obtained primary non woven fabric is excellent in a spinningproperty, however, depending on the kind of a lubricant, particularly inthe case of a fatty amide compound, it does not itself a static frictioncoefficient specified in the non woven fabric of the present invention,in some cases. In this case, for controlling the static frictioncoefficient of a non woven fabric in the range of from 0.1 to 0.4, itcannot be controlled in the range of static friction coefficientspecified in the present invention until treatment of this non wovenfabric under heat by an aging treatment. In conventional non wovenfabric production apparatuses, such an aging apparatus is notincorporated, and aging is not usually conducted.

[0057] Here, the aging treatment conditions vary depending on the kindof a polypropylene based resin, resin properties thereof such ascrystallinity, density, melting point and the like, the kind of a fattyamide compound contained, melting point and solubility in apolypropylene based resin (compatibility) thereof, and the like.Therefore, in view of the properties of a polypropylene based resin, rawmaterial for a non woven fabric and the properties of a fatty amidecompound as a lubricant, the static friction coefficient is in the rangefrom 0.1 to 0.4, and specifically determined experimentally in view ofproperties such as flexibility, feeling, skin tough feeling and the likerequired for the final product, and bending resistance thereof.

[0058] For example, the polypropylene based resin spun bonded non wovenfabric used in the present invention is obtained by an aging treatmentat temperatures of 30 to 60° C. for about 1 to 50 hours of a spun bondednon woven fabric obtained by melt spinning of a polypropylene basedresin containing a fatty amide compound.

[0059] For example, the following aging treatment conditions can be setspecifically when a homopolymer of propylene is used, the isotacticpentad fraction thereof is about 90 mol % and the content of erucicamide is 0.4 wt %.

[0060] When the aging temperature is 40° C., the aging time is fromabout 5 to 50 hours, preferably from about 8 to 24 hours. When the agingtime is 24 hours, the aging temperature is from about 32 to 50° C.,preferably from about 33 to 45° C. When the aging conditions are gentlerthan the above mentioned ranges, decrease in static friction coefficientrequires too much time, leading to lowering of productivity, in somecases. When the aging conditions are stricter than the above mentionedranges, the static friction coefficient increases conversely, beingundesirable in some cases.

[0061] This aging treatment can be usually conducted in an aging room inwhich non woven fabrics are wound in the form of roll and arranged oncore tubes and heated air is circulated. In this aging, even if nonwoven fabrics are wound in the form of roll, the non woven fabric canget a uniform aging treatment effect due to the gas permeability of thenon woven fabric. Further, not in the condition of wound non wovenfabric, but aging can also be conducted by roll heating and/or heatedair while running between rolls.

[0062] Next, another method of imparting a static friction coefficientto the polypropylene based resin spun bonded non woven fabricconstituting the multi layer non woven fabric of the present inventionis a method of surface treating fibers of the resulting non woven fabricby spinning. As the surface treatment agent, for example,dimethylsiloxane, methylhydrogenpolysiloxane, fatty amide containingcompounds, and the like can be used. However, this surface treatment hasproblems such as that treatment of inside is impossible, and the like,depending on wet treatment processes, drying processes and the thicknessof a non woven fabric, and the above mentioned method of melt mixing ofa lubricant is preferable in may cases depending on the form,application and the static friction coefficient range of a non wovenfabric, and the like.

[0063] The spun bonded non woven fabric made of a polypropylene basedresin constituting the non woven fabric laminate of the presentinvention is usually hydrophobic, and depending on applications ofabsorptive articles and the like, for example, in the case of use as atop material of disposable diapers and sanitary napkins, hydrophilicityis required for permeation of water, in some cases. In this case, a nonwoven fabric cannot be subjected to hydrophilicity imparting treatment.

[0064] Though this hydrophilicity imparting treatment includesintroduction of a hydrophilic group such as a carboxyl group and thelike by treatment with ozone, and surface treatment with a hydrophiliccompound, and from the standpoint of an effect, treatment with ahydrophilic compound solution is preferable. As the imparting treatmentmethod, a spray method, coating method, immersion method and the likeare exemplified. As the hydrophilic compound, for example, alkyl esterbased compounds such as polyhydric alcohols having 8 to 26 carbon atomscontaining polyoxyethylene, alkyl ether based compounds, fatty amidegroup containing polyethers, fatty monoglycerides, sorbitan esterderivatives, alkyl phosphate metal salts, alkyl sulfate metal salts,polyoxyethylene alkyl ether sulfate metal salts, alkyl sulfosuccinatemetal salts, saccharide derivatives having a glucose ring, and the likeare exemplified.

[0065] The spun bonded non woven fabric made of a polypropylene basedresin can get remarkably improved touch feelings such as flexibility,feeling, skin touch feeling and the like, and improved use feeling whilemaintaining essential properties of a non woven fabric of thepolypropylene based resin itself, namely, strength, heat resistance,bending resistance and the like, by decrease in static frictioncoefficient by this aging treatment and surface treatment.

[0066] Next, the polypropylene based resin melt blown non woven fabricconstituting the multi layer non woven fabric of the present inventionis a non woven fabric made of extremely fine fibers, and usually made offibers having a fiber diameter of 0.1 to 10 μm, preferably 0.2 to 6 μm,and has a mass per unit area of 1 to 45 g/m², preferably 2 to 30 g/m².These fiber diameter and mass per unit area significantly affect themoisture permeability, gas permeability, water resistance of a multilayer non woven fabric, the leak resistance of fine powders, and thelike, and can be appropriately selected within the above mentionedranges so that the required properties are satisfied by applications ofthe multi layer non woven fabric. For example, in the case of a sidegather of disposable diapers, it is from 1 to 5 g/m², and in the case ofa diaper back sheet and medical sheet, it is from 5 to 30 g/m².

[0067] The polypropylene based resin melt blown non woven fabric can beobtained by a known method in which heated gas flow of high seed isblown to fine stream of a melt polypropylene based resin, and by theaction of this gas flow, the melted resin is drawn to give extremelyfine fibers which are collected to be made into a sheet.

[0068] As the polypropylene based resin constituting this melt blown nonwoven fabric, the above mentioned polypropylene based resins used in thespun bonded non woven fabric can be used likewise. This polypropylenebased resin melt blown non woven fabric cannot necessarily be specifiedeasily, depending on the gas permeability, moisture permeability andwater preventing property of a multi layer non woven fabric andapplications of the multi layer non woven fabric of the presentinvention, and in general, the moisture permeability as the multi layernon woven fabric is usually 1000 g/m²·24 hours or more, preferably 2000g/m²·24 hours or more. The water preventing property (water pressureresistance) is, though different depending on applications thereof, 1kPa or more, preferably 10 kPa or more.

[0069] The multi layer non woven fabric of the present invention iscomposed of a plurality of layers of the specific polypropylene basedresin spun bonded non woven fabric and polypropylene based resin meltblown non woven fabric as described above. The method of laminating theboth non woven fabrics is not particularly restricted, and variousmethods can be adopted.

[0070] In the lamination method, usually, the above mentionedpolypropylene based resin spun bonded non woven fabric, for example,having been subjected to the aging treatment and having a staticfriction coefficient of 0.1 to 0.4 is laminated on and adheres to thepolypropylene based resin melt blown non woven fabric so that the spunbonded non woven fabric is situated at least one surface of the meltblown non woven fabric. However, in some cases, it is also possible thelaminate the spun bonded non woven fabric and the melt blown non wovenfabric before the aging treatment. In this case, listed is an inlinelamination method in which, for example, in spinning a melt blown nonwoven fabric on a spun bonded non woven fabric, and if necessary,further continuously producing spun bonded non woven fabrics on this ina several stages, a fatty amide is contained in the polypropylene basedresin for the spun bonded non woven fabric and a multi layer non wovenfabric is previously produced, then, this multi layer non woven fabricis subjected to aging treatment.

[0071] As the lamination means for obtaining this multi layer non wovenfabric, various lamination means such as heat adhesion, adhesion withadhesives and the like are mentioned, and there can be adopted the abovementioned inline lamination heat adhesion means which are simple andcheap, particularly, a heat emboss roll method. In this heat emboss rollmethod, lamination can be conducted using a known lamination apparatushaving an emboss roll and a flat roll. Here, as the emboss roll, embosspatterns of various forms can be adopted, and lattice form in whichfusion parts are continuous, lattice form in which fusion parts aredependent, arbitrary distribution and the like are mentioned. The embossarea ratio is in the range of from about 5 to 40%. These embosspatterns, emboss area ratio, temperature, pressure and the like can beappropriately selected depending on the fiber diameter, thickness, massper unit area, layer ratio, gas permeability, processing speed and thelike of a non woven fabric.

[0072] In the dry laminate method, it is important to secure themoisture permeability and gas permeability of the non woven fabriclaminate of the present invention at certain levels or more, and it isnecessary to control them by the coated amount of a hot melt adhesivecoated on the lamination surface, the existence ratio of adhesionpoints, and the like. Specifically, the amount of a hot melt adhesive isfrom 0.1 to 5 g/m², and as the coating method, it is preferable to adoptnot a usual coating means but a means capable of spraying in the form offiber to give partial adhesion. As the adhesive in this case, ethylenevinyl acetate based adhesives, polyurethane based adhesives, polyesterbased adhesives and the like are used. A method of coating an adhesivein the form of patterns and conducting dry laminating can also beadopted.

[0073] The multi layer non woven fabric of the present invention ismainly composed of a polypropylene based resin spun bonded non wovenfabric, and specifically, spun bonded non woven fabric:melt blown nonwoven fabric (mass per unit area) is 95:5 to 60:40, preferably 90:10 to75:25. Namely, the main part of the multi layer non woven fabric is madeof a spun bonded non woven fabric, and flexibility, feeling and skintouch thereof are remarkably improved by basic properties such as thestrength, elastic modulus and the like of a spun bonded non woven fabricand by complexing of a slight proportion of melt blown non woven fabric.

[0074] The multi layer non woven fabric of the present invention canalso be made of two layers as described above. In this case, however,the problems of surface conditions of a melt blown non woven fabricstill remain. For this, use positions and applications thereof arenaturally limited. Therefore, it is preferable to give a three layerstructure in which a melt blown non woven fabric is sandwiched by spunbonded non woven fabrics. In this case, depending on applications, thelayer ratio of the spun bonded non woven fabrics in the both outerlayers can be appropriately changed.

[0075] The multi layer non woven fabric of the present invention can bemade as a multi layer non woven fabric having various properties byselection and combination of the kinds, mass per unit area, thickness,gas permeability, moisture permeability and the like of a polypropylenebased resin spun bonded non woven fabric and a polypropylene based resinmelt blown non woven fabric. Therefore, gas permeability, moisturepermeability, water preventing property and finer powder barrierresistance are established simultaneously, and additionally, excellentproperties such as strength, flexibility, feeling, skin touch feelingand the like and secondary processabilities because of excellentstiffness are satisfied together, and development into variousapplications is possible. Specifically, the multi layer non woven fabriccan be effectively used for back sheets and side gathers of absorptivearticles (hygienic articles) such as disposable diapers, sanitarynapkins, incontinence pads and the like, powder wrapping materials,medical sheets and the like having functions such as moisture absorbingagents, de-oxygen agents, de-odoring agents and the like.

[0076] The multi layer non woven fabric of the present invention will beillustrated in detail below based on one production example, but thescope of the invention is not limited to the examples.

EXAMPLE 1 Inline Production of Multi Layer Non Woven Fabric

[0077] As the non woven fabric production apparatus, that of multi stagemode was used. Into 100 parts by weight of a crystalline polypropyleneresin [isotactic pentad fraction: 91 mol %, MFR: 60 g/10 minutes,melting point: 160° C.] was dry blended 0.035 parts by weight of aphenol based antioxidant (manufactured by Chiba Specialty Chemicals,Irganox 1010), 0.035 parts by weight of a phosphorus based antioxidant(manufactured by Sand, Sandstub P-EPQ), 0.025 parts by weight of aneutralization agent (manufactured by Kyodo Yakuhin K.K., calciumstearate) and 0.4 parts by weight of erucic amide, by a super mixer,then, the mixture was melt kneaded at 220° C. using a 65 mm φ extrusionmolding machine, and extruded through a spinning mouth ring, for meltspinning. The spinning mouth rings in this case have a caliber of 0.3 mmand 200 rings were arranged along the width direction and 15 rings werearranged along the extrusion direction.

[0078] Then, the spun fibers were introduced into an air sucker andtraction stretched, and collected on a belt having a suction apparatus.On this polypropylene spun bonded non woven fabric, a melt blown nonwoven fabric was formed by the above mentioned crystalline polypropyleneresin containing no erucic amide, then, further, on this was laminatedthe same polypropylene spun bonded non woven fabric as described above,subsequently, transferred to a heat emboss roller, and emboss adheredunder emboss conditions shown in Table 1, and taken on a paper tube, toobtain a primary multi layer non woven fabric composed of three layersof spun bonded non woven fabric/melt blown non woven fabric/spun bondednon woven fabric.

[0079] The resulted taken multi layer non woven fabric was subjected toaging treatment under aging conditions [temperature: 40° C., 24 hours]to obtain a three layer non woven fabric of the present invention.Thread cut and rolling were not found in the spinning process, and anexcellent spinning property was shown. Further, controlling the spinningconditions, a three layer non woven fabric was obtained composed of aspun bonded non woven fabric [average fiber diameter: 17 μm, mass perunit area: 7 g/m²] and a melt blown non woven fabric [average fiberdiameter: 1 μm, mass per unit area: 3 g/m²] and having a total mass perunit area of 17 g/m². The multi layer non woven fabric, productionconditions are shown in table 1 and property evaluation results andsecondary processabily are shown in Table 2. The evaluation of the multilayer non woven fabric was conducted based on the followingdescriptions.

[0080] (1) Static Friction Coefficient

[0081] It was measured according to the static friction coefficientmeasurement method of ASTM-D1894. For details, see the above mentioneddescriptions.

[0082] (2) Bending Resistance [Total of Longitudinal and Transversal]

[0083] It was measured according to JIS L 1096 6. 19. 1 A method (45°cantilever method).

[0084] (3) Feeling

[0085] A functional test was conducted by skin tough and hand tough by20 monitors, and evaluated by ⊚, ◯ and Δ. In the functional test, thesame three layer non woven fabric using a usual spun bonded non wovenfabric containing no erucic amide (Comparative Example 1) was evaluatedas Δ.

[0086] (4) Water Pressure Resistance

[0087] It was measured according to JIS L 1092 (high water pressuremethod).

[0088] (5) Secondary Procesability

[0089] A hot melt type adhesive containing ethylene vinyl acetate“H-6805” [manufactured by Nitta Findray K.K.] was sprayed in the form offiber on a polypropylene multi layer non woven fabric using a fiberspray die of nozzle discharge mode so that the coating amount was 4g/m². Then, on this, an inorganic filler containing stretched PEmoisture permeable film “Polam PU35” (thickness: 35 μm) manufactured byTokuyama K.K. was pasted overlapping to product a non woven fabriclaminate. In establishing this pasting, wrinkling, meandering andpowdering was evaluated as Δ and processing without problems wasevaluated as ⊚.

COMPARATIVE EXAMPLE 1

[0090] A three layer non woven fabric was obtained in the same manner asin Example 1 except that addition of erucic amide and aging treatmentwere not conducted in Example 1. The multi layer non woven fabric,production conditions according to Example 1 are shown in Table 1, andthe property evaluation results and secondary processability are shownin Table 2.

COMPARATIVE EXAMPLE 2

[0091] Using the polypropylene based resin containing no erucic amideused in Example 1, a single layer spun bonded non woven fabric (no agingtreatment) was obtained. The non woven fabric, production conditionsaccording to Example 1 are shown in Table 1, and the property evaluationresults and secondary processability are shown in Table 2.

COMPARATIVE EXAMPLE 3

[0092] A single layer spun bonded non woven fabric (no aging treatment)was obtained except that the fiber diameter and mass per unit area werechanged in Comparative Example 2. The non woven fabric, productionconditions are shown in Table 1, and the property evaluation results andsecondary processability are shown in Table 2.

[0093] These results show that the present invention shows significantlylowered bending resistance and significantly improved flexibility,feeling and skin tough as compared with Comparative Example 1. This ismore than a non woven fabric obtained by compounding a thermoplasticelastomer in fair amount into a polypropylene based resin. Additionally,the secondary processability is equivalent. In comparison with thesingle layer spun bonded non woven fabric of Comparative Example 2, itis apparent that when the fiber diameter is decreased, the bendingresistance can be decreased, however, simultaneous satisfaction with thesecondary processability is impossible. Further, in comparison withComparative Example 3, it is apparent that it is necessary to maintainfiber diameter and mass per unit area at certain levels for satisfyingthe secondary processbaility, and it is apparent that it is difficult tosatisfy the secondary processability and flexibility, feeling and skintouch feeling simultaneously by these methods. TABLE 1 Layer Embossconditions constitution Temperature * Mass per Area (° C.) Fiberdiameter unit area ratio Pressure Emboss side/ (μm) (g/m²) % N/cm flatside Example 1 S/M/S 7/3/7 20 500 135/135 17/1/17 Comparative S/M/S7/3/7 20 500 135/135 example 1 17/1/17 Comparative S 17 20 500 130/130example 2 14 Comparative S 18 20 500 135/135 example 3 18

[0094] TABLE 2 Bending Water Static resistance(mm) pressure Secondaryfriction Longi- Trans- Feel- resistance process- coefficient tudinalversal Total ing mmH₂O ability Example 1 0.29 42 39 81 ⊚ 105 ⊚Comparative 0.60 65 35 100 Δ 108 ⊚ example 1 Comparative 0.55 43 20 63 ⊚60 Δ example 2 Comparative 0.62 57 38 95 Δ 68 ⊚ example 3

INDUSTRIAL APPLICABILITY

[0095] The multi layer non woven fabric obtained by complexing a spunbonded non woven fabric and a melt blown non woven fabric, made ofpolypropylene based resins can be suitably used for variousapplications, particularly, back sheet materials and side gathermaterials for absorptive articles such as disposable diapers, sanitarynapkins and the like, and for medical materials, powder wrappingmaterials and the like.

1. A multi layer non woven fabric having a polypropylene based resinspun bonded non woven fabric and a polypropylene based resin melt blownnon woven fabric, characterized in that it has a bending resistance [thesum of the values for longitudinal and transverse directions as measuredaccording to JIS L 1096
 6. 19.1 A method (45° cantilever method)] of 70to 120 mm, and the surface of the spun bonded non woven fabric has astatic friction coefficient of 0.1 to 0.4.
 2. The multi layer non wovenfabric according to claim 1 wherein the multi layer non woven fabric hasa polypropylene based resin melt blown non woven fabric betweenpropylene based resin spun bonded non woven fabrics.
 3. The multi layernon woven fabric according to claim 1 or 2 wherein the spun bonded nonwoven fabric has an average fiber diameter of 10 to 30 μm and the massper unit area of the multi layer non woven fabric is from 10 to 50 g/m².4. The multi layer non woven fabric according to any of claims 1 to 3wherein the spun bonded non woven fabric contains a lubricant in anamount of 0.05 to 1.0% by weight.
 5. The multi layer non woven fabricaccording to any of claims 1 to 4 wherein the lubricant is a fatty amidecompound.
 6. An absorptive article obtained by using the multi layer nonwoven fabric according to any of claims 1 to
 5. 7. A medical sheetobtained by using the multi layer non woven fabric according to any ofclaims 1 to
 5. 8. A powder wrapping material obtained by using the multilayer non woven fabric according to any of claims 1 to 5.